Acoustic Design for Offices: Absorption, Separation and Masking

Three levers, used together

Lever	What it does	Where it applies
Absorption	Stops sound building up within a space	Open plan, any room
Separation	Stops sound passing between spaces	Enclosed rooms
Masking	Reduces intelligibility of what remains	Large open floors

Most offices apply absorption partially, separation incompletely, and masking not at all — then wonder why the space is tiring.

Absorption: the ceiling does most of the work

In an open-plan floor the ceiling is the largest uninterrupted surface and it faces everyone. An absorbent ceiling contributes more than any other single element.

The modern problem is that three fashionable choices each remove an absorbent surface:

• Exposed soffit instead of a suspended absorbent ceiling
• Glazed partitions instead of solid walls
• Hard flooring instead of carpet

Each is defensible. Together they leave a room with almost nothing to absorb sound. If those choices are wanted, absorption must be reintroduced deliberately — acoustic rafts or baffles beneath the soffit, wall panels, or carpet in the working zones.

Absorption performance comes from data measured under ISO 354, and the required quantity is calculable at design stage from room volume and surface areas.

Separation: the partition is not the problem

The recurring failure in meeting rooms is flanking — sound going around the wall rather than through it.

In order of impact:

1. Take the partition to the slab, or build an acoustic barrier above the ceiling line
2. Seal every junction — head, base, abutments — continuously
3. Treat services crossings — ducts, trays, pipes, sleeves
4. Offset back-to-back outlets so they do not share a stud cavity
5. Then consider upgrading the partition itself

Most projects do step five and skip one to four. Sound insulation is rated under ISO 717-1, and a laboratory rating describes a partition tested without flanking — which the building will not reproduce.

Masking: the lever nobody uses

On a large open floor, absorption alone often cannot make speech from neighbouring desks unintelligible. Masking addresses that directly by raising the background very slightly with a shaped, unobtrusive sound.

Done well it is unnoticeable and effective. Done badly — uneven coverage, an audible hiss, the wrong spectrum — it is worse than nothing, so it needs designing and commissioning rather than installing.

ISO 3382-3 addresses the measures that describe open-plan conditions, including how far speech remains intelligible across a floor.

Services noise

Frequently overlooked, and it sets the background the rest of the design works against:

• Fan coil units directly above occupants — check sound data, not just capacity
• Air velocity through ducts and grilles
• Oversized equipment running hard to meet a setpoint
• Vibration transmitted through structure and hangers

Noise control provisions for building services sit within NBC 2016, Part 8.

The practical sequence

1. Decide which rooms genuinely need privacy — usually fewer than requested
2. Treat those completely: partition to slab, junctions sealed, services treated
3. Get absorption right in the open plan, ceiling first, then floor
4. Check services noise as part of equipment selection
5. Consider masking if the floor is large and privacy is still inadequate

Standards referenced

Open-plan office acoustics in ISO 3382-3; sound insulation rating in ISO 717-1; sound absorption measurement in ISO 354; services noise control provisions in NBC 2016, Part 8. Acoustic targets and treatment for a specific project must be established by the project's acoustic consultant.